Analyze this
 

Ok, I asked this question already, but I am going to to repeat it because of the lack of answers and the current info. (not trying to offend)

I have a 2003 Hummer with 107+k on it. It is stock.
Not long ago I started to see what looks like a whitish to tannish color smoke come from the rear when I exited off the interstate after traveling for 1.5 hours at 85 mph in the southern heat and humidity. There is a kind of chemical smell to it. I thought it was brake dust at first. Ok, well I have noticed that it will do the above mentioned 2-3 times each time I hit the brakes as I stopping hard. If I try to just slow down and do a gradual stop, it doesnt happen (or at least I cant see it). Around town it doesnt smoke, maybe once or twice if I am cruising for little bit and have to hit the brakes hard, but normal driving.... nothing. If i sit in my driveway and run the engine to about 2-3k for a few minutes and then release the pedal. Nothing. I dont even see anything leak. I have even tried revving to 2-3k and depressing the brakes hard in the drive way. Nothing.
I have put some no smoke additive in with no results.
Now i also cant be sure but I dont think this happened before the a/c was recharged (I know recharging is BS, but my mechanic said he had to to find the leak because the leak was so small - that was about 3 months ago and i still have a/c).
Also, the only thing i see dripping from my engine area at any time is ALOT of water. In fact after the long drive i pull into the driveway and look and there is alot of water dripping to the ground and when i look in the wheel well there is alot of water on the frame and what looks to be the engine (though the early morning and the lack of sleep is fogging my memory a little).

I can not seem to duplicate this unless i am going a decent rate of speed and then brake hard.
given it doesnt look like brake dust since at times i have seen it come up from the sides.

also currently my mechanic has told me that my cats are bad. he said this since when i brought it in i told him about the rattle can sound that comes from the under of the car that at times will come and go and disappear something after the truck has been running awhile. without hesitation he stated those are bad cats.
so there is another issue to think about

any ideas

Re: Analyze this
 

Are you sure the water isn't AC condensation run off? Hard braking might make the condenser drip on the exhaust pipes??? I'd definitely get a second or third opinion on the cats. This might be one of the few things I'd take it to the dealer to analyze and then think about having an Indy repair it, or fix it yourself. When the H2 first came out, there were lots of rattle issues with the exhaust tubing on 2003s and 04s.

Re: Analyze this
 

Hummer Jim,
It is a good possibility that the water is AC condensation, but could that be causing the whitish/ tannish smoke?

Also, the mechanic that diagnosed my cats actually is a dealership mechanic for Cheyy/ GMC

Given, the rattle issues wouldnt they sound more like pipes banging?
This actually sounds like you put rocks in a soda can and then you are shaking the soda can

Re: Analyze this
 

The exhaust on the 2003 and 04 really can make several odd vibrations and pops and creaking noises but if you are hitting the cats while they are cold and the have a rattle they sound like they are going bad then.


Could the smoke from the brakes be brake dust?
Not sure but it sounds like ceramic pads and shoes are wearing out and dusting. Since you said this only happens at high speed braking and it is not from the tail pipe.

~Richard